In this work, the properties of marine algae Gelidium, algal waste from agar extraction industry and a
composite material were investigated for cadmium(II) biosorption. Equilibrium experiments were performed
at three pH values (4, 5.3 and 6.5). Equilibrium data were well described by the Langmuir and
Langmuir–Freundlich isotherms. Two models predicting the pH influence in the cadmium biosorption
(discrete and continuous models) have been developed in order to better describe the equilibrium. The
continuous model also considers a heterogeneous distribution of carboxylic groups, determined by potentiometric
titration. The results of batch kinetic experiments performed at different pH values were well
fitted by two mass transfer models and the homogeneous diffusion coefficients for the cadmium ions
inside the biosorbentwere obtained. Continuous stirred tank reactor (CSTR) and packed bed column configurationswere
also examined for the biosorption of cadmium ions. A strong acid (0.1MHNO3)was used
as eluant to regenerate the biosorbents in the column. Several mass transfer models were applied with
success to describe the biosorption process in batch mode, CSTR and fixed bed column.